As is well known to those skilled in the art, in order to heat rapidly the mass of a fuel processor to its proper operating temperature during a startup cycle, it is preferable to provide the largest possible heating gas flow therethrough. However, using fuel rich-combustion gas flow may exceed the temperature limits in the earlier stages of the fuel processor, thereby requiring additional stages to fully heat the remaining stages of the fuel processor.
During a shut down cycle, it is desirable to remove water from the fuel processor so that the water does not condense onto the catalysts when the fuel processor completely cools, which may damage the catalysts. Furthermore, it is also desirable to stop the fuel processor in a pressurized state so that when the fuel processor cools and the gases contract, the pressure the fuel processor remains above atmospheric pressure so that air is not drawn into the fuel processor. Conventional shut down methods cannot continue operating without water injection, as the ATR catalyst would get too hot.
During a turn down cycle, it is preferable to circulate a larger flow so that the residence times within the reactors are more constant. However, in conventional fuel processors, as the power level is turned down the flow is thus reduced and the residence times in each reactor increases. This increase in residence times may lead to auto-ignition in the inlet, reverse water gas shift in the PrOx, cell reversal in fuel cell stack due to non-uniform flow distribution of hydrogen containing reformate, and water collection in fuel cell stack.
During a transient cycle, it is preferable to have a constant flow through the reactors such that the pressure in the reactors remains generally constant, thereby minimizing the lag in transient response associated with filling or venting volumes of the fuel processor.
Accordingly, there exists a need in the relevant art to provide a fuel processor that is capable of rapid thermal start without the complexity of multiple stages or risk of oxygen exposure. Furthermore, there exists a need in the relevant art to provide a fuel processor that, during shut down, is capable of minimizing water in the reformate and be shut down at an elevated pressure to minimize condensation on the catalyst and air ingestion upon cooling. Still further, there exists a need in the relevant art to provide a fuel processor that, during turn down, is capable of minimizing auto-ignition in the inlet, reverse water gas shift in the PrOx, cell reversal in fuel cell stack due to non-uniform flow distribution of hydrogen containing reformate, and water collection in fuel cell stack. Yet further, there exists a need in the relevant art to provide a fuel processor that, during transient operation, is capable of maintaining a generally constant flow rate through to the fuel processor to minimize the lag time associated with filling or venting volumes of the fuel processor. Still further, there exists a need in the relevant art to provide a fuel processor that is capable of operating without water injection.